Artificial ponds inhabited by fishes and other aquatic life are a frequent feature of parks, golf courses and other public facilities, while some private homes also have ornamental ponds with carp, goldfish or the like. The matter excreted and secreted by the fishes and the uneaten portion of the fish food supplied to the pond deplete the oxygen content of the water and promote proliferation of various pathogenic fungi and bacteria, producing an unhealthy environment for the fishes. Various systems have been developed for purifying such pond water using physical (mechanical) means such as filters, chemical processes, or both.
JP-A-62-204814, for instance, discloses a purifier using only physical means, i.e., a filter, while JP-B-49-29517 discloses a pond system that combines physical and chemical means.
All such conventional pond water purification technologies are, however, deficient in the point of not adequately utilizing the purification system of the natural environment described in the following.
The system of JP-A-62-204814 constantly operates a suction pump so as to deposit foreign matter in the water in a filter layer consisting of gravel or the like. The water is further passed through a water passage chamber, a deep region and a suction chamber installed at the bottom of the pond to remove foreign matter with a filter and is then passed through the suction pump and returned to the pond from an outlet. Since the system is not configured to utilize the natural purification system, however, the pond structure is complex and a high-horsepower suction pump must be used.
The system of JP-B-49-29517 effects physical filtering in a tank filter to remove solid particles (impurities), thereafter effects biochemical purification in a sedimentation tank, and then returns the purified water to the pond. This system also has to be large and complex because it does not utilize the purification system of the natural environment.
These pond water purification systems are further liable to allow alga cells and the like to stick to the bottom of the pond where they may rapidly proliferate when the environmental conditions become right. When this happens, the color of the pond water changes and algae may make the pond environment unsuitable for animal life.